2 Answers
2

The French side has a lot of conflicting estimates of size, but by all accounts was very heavily weighted toward men-at-arms. Estimates generally run north of 10,000, with only about 5,000 archers and crossbow. That would give us a ratio of somewhere between 1 or 2 knights per archer/bowman. (At least one other source numbers the total French army at 50,000 with the rearguard added in, but said that they wouldn't let the archers participate, for fear of friendly fire).

Of course this battle is rather famous as an example of how immense numbers of knights could be slaughtered by longbowmen if conditions are right. The French of this period were rather enamored of impulsive ill-advised mounted charges (see also Crecy, Poitiers, Nicopolis), while English knew how to use that against them, often chosing a very good defensive position with large numbers of men-at-arms fighting unmounted.

Note that the term man-at-arms is sometimes used interchangably with Knight, and sometimes not. Figuring if your intended meaning matches with that of the particular medieval chorniclers in question would be a difficult task.
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T.E.D.♦Feb 14 '13 at 19:35

3

Knights certainly were man-at-arms, not all men-at-arms were knights
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spyderFeb 15 '13 at 3:53

3

indeed, and in the vocabulary of the era a man-at-arms was not a knight, he was a conscript soldier, usually a peasant or city dweller in service to a nobleman who would be the knight. The actual number of knights was far lower, probably no more than a few dozen. Think the ratio of tanks to total manpower in the modern US Army.
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jwentingFeb 15 '13 at 8:07

The equipment for a knight was very expensive to create and maintain, it was therefore reserved for the rich, the nobility. Those were of course also the main group of people who could afford horses trained for riding as warhorses (which is quite different training from general riding and draft horses), so my guess is it would be unlikely to see a knight on foot if there were a need for cavalry in an engagement.
Now, as to ratios, that's probably hard to tell. But I'd venture a guess of each knight/nobleman bringing from several dozen to several hundred men at arms depending on time of year, length of expected campaign, wealth and size of his holdings, etc. etc.
Mind that these things were not constant. Over time the more powerful "countries" would start equipping standing armies, the overlord paying for equipment and training of regiments of knights who had themselves no land holdings and subservient people providing manpower for them.http://en.wikipedia.org/wiki/Medieval_warfare has information, without mentioning numbers (and I'm not sure I agree with all of it, it seems to put too much authority in romantic novels and over exaggerating the number of knights as a result).http://forums.randi.org/showthread.php?t=200812 has interesting information as well